Technical Field
The present subject matter relates to the field of devices for tolling or telematics systems. In particular, the present subject matter relates to a device which is provided with a pixel based image sensor wherein the image sensor is adapted to be arranged above a surveillance zone provided on a road. The surveillance zone has an extension along the direction of the road, and the image sensor is adapted to be arranged in between a first and a second end zone of the surveillance zone.
Background Art
Road tolling systems are used to detect and register vehicles that are utilizing a road that is subjected to toll fees, sometimes in terms of tax. The most commonly used road tolling systems comprise a gantry with several devices, including a transceiver and sensors, arranged onto it. The transceiver is used for automatic registration of passing vehicles with transponders. Vehicles with transponders are automatically tolled each time they pass a road toll station. The sensors, preferably cameras, are used to capture images of the license plates of passing vehicles without transponders. Depending on the system concept the images can be used to perform tolling based on the license plate number or serve as an evidence of non-compliance in the case transponders are required.
Commonly, two cameras are arranged as a pair on the gantry and positioned to capture one lane of the surveillance zone. The first of the two cameras is directed towards a first end zone wherein vehicles are entering the surveillance zone and the second of the two cameras is directed towards a second end zone wherein the vehicles are exiting the surveillance zone. The cameras are focused at a preset height above the road corresponding to the height of the license plate of the passing vehicles. The height is preset based on the most common height of license plates on a standard vehicle. The images that are captured by the cameras are normally processed in an ANPR (automatic number plate recognition) system.
As described in U.S. Pat. No. 6,959,869 B the cameras capture the front and rear license plate numbers and the numbers are automatically matched to each other by a control device such as a computer. With this system, at least two cameras are needed to capture both the front license plate and the rear license plate. A transceiver is also needed for the automatic reading and tracking of transponders. Hence, several separate devices are used for vehicle detection, tracking and registration which increase the cost of the road tolling systems and increase the visual impact of the gantry with several devices mounted thereon.
With systems as described above, a tracking system utilized between the capturing zones is needed to ensure that the images captured by the two cameras can be linked to the same vehicle.
Devices are often also needed for vehicle classification based on physical characteristics such as size or volume of the vehicle.